Low emission propylene homopolymer with high melt flow

ABSTRACT

Propylene homopolymer with reduced emission value and high melt flow rate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is the U.S. national phase of InternationalApplication No. PCT/EP2014/075054, filed on Nov. 19, 2014, which claimsthe benefit of European Patent Application No. 13194123.9, filed Nov.22, 2013, the disclosures of which are incorporated herein by referencein their entireties for all purposes.

The present invention is directed to a new propylene homopolymer withreduced emissions as well as to its manufacture and use.

Polypropylene is used in many applications. Depending on its endapplications the properties of the polypropylene must be tailoredaccordingly. For instance some end applications require very stiffmaterial. Further nowadays the polymer processors desire material withlow emissions to fulfil the consistently rising demands of regulatoryauthorities as well as consumers.

Typically, adsorbing additives are used to achieve low emission values.For instance in WO 2011/023594 melamine is employed to obtain polymermaterial with reduced emission values. In WO 92/13029 A1 zeolites areused for the same purpose. Two disadvantages of these solutionsemploying absorbing additive particles are the parallel absorption ofantioxidants and the unsuitability for film and fibre applications.

Thus the object of the present invention is to provide a polymermaterial which is rather stiff and characterized by low emissions.

The finding of the present invention is that a propylene homopolymermust be produced with a Ziegler-Natta catalyst containing an internaldonor (ID) not belonging to the class of phthalic acid ester. With sucha catalyst propylene homopolymer can be produced having excellentstiffness and low emission values.

Thus the present invention is directed to a propylene homopolymer having

-   (a) a melt flow rate MFR₂ (230° C./2.16 kg) measured according to    ISO 1133 in the range of 75.0 to 500 g/10 min; and-   (b) a pentad isotacticity (mmmm) of more than 90.0% determined by    ¹³C-NMR;

wherein further

-   (c) the propylene homopolymer fulfills inequation (I)    VOC≦(MFR×0.08)+201.0    -   wherein    -   VOC is the amount of volatile organic compounds (VOC) [in ppm]        measured according to VDA 278:2002 of the propylene homopolymer;    -   MFR is the melt flow rate MFR₂ (230° C./2.16 kg) measured        according to ISO 1133 of the propylene homopolymer, and-   (d) preferably the propylene homopolymer has a melting temperature    Tm of equal or more than 160° C.

In one preferred embodiment the propylene homopolymer according to thisinvention has a VOC value measured according to VDA 278:2002 of equal orbelow 210 ppm.

Additionally or alternatively to the VOC value, the propylenehomopolymer according to this invention can be also characterized by itsFOG value. Accordingly it is preferred that the propylene homopolymerfulfills inequation (II)FOG≦(MFR×1.26)+350.0

wherein

FOG is the amount of fogging compounds (FOG) [in ppm] measured accordingto VDA 278:2002 of the propylene homopolymer, preferably of thepropylene homopolymer in form of pellets; and

MFR is the melt flow rate MFR₂ (230° C./2.16 kg) measured according toISO 113 of the propylene homopolymer.

In one preferred embodiment the propylene homopolymer according to thisinvention has a FOG value measured according to VDA 278:2002 of not morethan 580 ppm.

Preferably the propylene homopolymer according to this invention has acrystallization temperature of equal or more than 114° C.

In another preferred embodiment the propylene homopolymer according tothis invention has a xylene cold soluble content (XCS) determinedaccording ISO 16152 (25° C.) of at least 1.8 wt.-%, preferably in therange of 1.8 to 5.5 wt.-%.

It is in particular preferred that the propylene homopolymer accordingto this invention has 2,1 erythro regio-defects of equal or below 0.4mol.-% determined by ¹³C-NMR spectroscopy and/or a pentad isotacticity(mmmm) of more than 93.0%.

It is further preferred that the propylene homopolymer according to thisinvention has a tensile modulus measured at 23° C. according to ISO527-1 (cross head speed 1 mm/min) of at least 1,500 MPa.

The present invention is also directed to an article comprising thepropylene homopolymer as described herein.

The present invention is also directed to the manufacture of thepropylene homopolymer as defined herein, wherein said propylenehomopolymer is obtained by polymerizing propylene in the presence of

-   (a) a Ziegler-Natta catalyst (ZN-C) comprising compounds (TC) of a    transition metal of Group 4 to 6 of IUPAC, a Group 2 metal    compound (MC) and an internal donor (ID), wherein said internal    donor (ID) is a non-phthalic compound, preferably is a non-phthalic    acid ester;-   (b) optionally a co-catalyst (Co), and-   (c) optionally an external donor (ED).

It is in particular preferred that

-   (a) the internal donor (ID) is selected from optionally substituted    malonates, maleates, succinates, glutarates,    cyclohexene-1,2-dicarboxylates, benzoates and derivatives and/or    mixtures thereof, preferably the internal donor (ID) is a    citraconate;

and/or

-   (b) the molar ratio of co-catalyst (Co) to external donor (ED)    [Co/ED] is 5 to 45.

In one preferred embodiment the propylene homopolymer is produced in asequential polymerization process comprising at least two reactors (R1)and (R2), in the first reactor (R1) a first propylene homopolymerfraction (H-PP1) is produced and subsequently transferred into thesecond reactor (R2), in the second reactor (R2) a second propylenehomopolymer fraction (H-PP2) is produced in the presence of the firstpropylene homopolymer fraction (H-PP1), wherein a catalyst is used asdefined above and in more detail below.

In the following the invention is described in more detail.

According to the present invention the expression “propylenehomopolymer” relates to a polypropylene that consists substantially,i.e. of at least 99.0 wt.-%, more preferably of at least 99.5 wt.-%,still more preferably of at least 99.8 wt.-%, like of at least 99.9wt.-%, of propylene units. In another embodiment only propylene unitsare detectable, i.e. only propylene has been polymerized.

One requirement of the propylene homopolymer according to this inventionis its melt flow rate. Accordingly the propylene homopolymer has an MFR₂(230° C./2.16 kg) measured according to ISO 1133 in the range of 75.0 to500 g/10 min, preferably in the range of 79.0 to 400 g/10 min, morepreferably in the range of 80.0 to 350.0 g/10 min, like in the range of81.0 to 300 g/10 min.

The propylene homopolymer is especially featured by its low emissions.Contrary to the propylene homopolymers known in the art the emissionsare rather low at a specific molecular weight compared to knownproducts. Thus the propylene homopolymer fulfills inequation (I), morepreferably inequation (Ia),VOC≦(MFR×0.08)+201.0  (I)VOC≦(MFR×0.08)+170.0  (Ia)VOC≦(MFR×0.08)+150.0  (Ib)VOC≦(MFR×0.08)+135.0  (Ia)

wherein

VOC is the amount of volatile organic compounds (VOC) [in ppm] measuredaccording to VDA 278:2002 of the propylene homopolymer, preferably ofthe propylene homopolymer in form of pellets; and

MFR is the melt flow rate MFR₂ (230° C./2.16 kg) measured according toISO 113 of the propylene homopolymer.

Preferably the amount of volatile organic compounds (VOC) measuredaccording to VDA 278:2002 of propylene homopolymer is equal or below 215ppm, more preferably equal or below 180 ppm, like equal or below 160ppm.

The VOC values are measured on pellets as defined in detail below.However also the VOC values measured on plates are reduced vis-à-vis thestate of the art (see examples).

Additionally or alternatively to the VOC value, the propylenehomopolymer according to this invention preferably fulfills inequation(II), more preferably inequation (IIa), still more preferably inequation(IIb),FOG≦(MFR×1.26)+350.0  (II)FOG≦(MFR×1.26)+330.0  (IIa)FOG≦(MFR×1.26)+320.0  (IIb)

wherein

FOG is the amount of fogging compounds (FOG) [in ppm] measured accordingto VDA 278:2002 of the propylene homopolymer, preferably of thepropylene homopolymer in form of pellets; and

MFR is the melt flow rate MFR₂ (230° C./2.16 kg) measured according toISO 113 of the propylene homopolymer.

Preferably the amount of fogging compounds (FOG) measured according toVDA 278:2002 of propylene homopolymer is not more than 590 ppm, morepreferably not more than 580 ppm.

The FOG values are measured on pellets as defined in detail below.However also the FOG values measured on plates are reduced vis-à-vis thestate of the art (see examples).

The propylene homopolymer is further defined by its microstructure.

Preferably the propylene homopolymer is isotactic. Accordingly it ispreferred that the propylene homopolymer has a rather high pentadconcentration (mmmm %), determined by ¹³C-NMR spectroscopy, i.e. morethan 93.0%, more preferably more than 93.5%, like more than 93.5 to97.5%, still more preferably at least 95.0%, like in the range of 95.0to 97.5%.

A further characteristic of the propylene homopolymer is the low amountof misinsertions of propylene within the polymer chain, which indicatesthat the propylene homopolymer is produced in the presence of aZiegler-Natta catalyst, preferably in the presence of a Ziegler-Nattacatalyst (ZN-C) as defined in more detail below. Accordingly thepropylene homopolymer is preferably featured by low amount of 2,1erythro regio-defects, i.e. of equal or below 0.4 mol.-%, morepreferably of equal or below than 0.2 mol.-%, like of not more than 0.1mol.-%, determined by ¹³C-NMR spectroscopy. In an especially preferredembodiment no 2,1 erythro regio-defects are detectable.

It is preferred that the propylene homopolymer according to thisinvention is featured by rather high cold xylene soluble (XCS) content,i.e. by a xylene cold soluble (XCS) of at least 1.8 wt.-%, like at least2.0 wt.-%. Accordingly the propylene homopolymer has preferably a xylenecold soluble content (XCS) in the range of 1.8 to 5.5 wt.-%, morepreferably in the range of 2.0 to 5.0 wt.-%, still more preferably inthe range of 2.2 to 5.0 wt.-%.

The amount of xylene cold solubles (XCS) additionally indicates that thepropylene homopolymer is preferably free of any elastomeric polymercomponent, like an ethylene propylene rubber. In other words, thepropylene homopolymer shall be not a heterophasic polypropylene, i.e. asystem consisting of a polypropylene matrix in which an elastomericphase is dispersed. Such systems are featured by a rather high xylenecold soluble content.

The amount of xylene cold solubles (XCS) additionally indicates that thepropylene homopolymer preferably does not contain elastomeric(co)polymers forming inclusions as a second phase for improvingmechanical properties. A polymer containing elastomeric (co)polymers asinsertions of a second phase would by contrast be called heterophasicand is preferably not part of the present invention. The presence ofsecond phases or the so called inclusions are for instance visible byhigh resolution microscopy, like electron microscopy or atomic forcemicroscopy, or by dynamic mechanical thermal analysis (DMTA).Specifically in DMTA the presence of a multiphase structure can beidentified by the presence of at least two distinct glass transitiontemperatures.

Accordingly it is preferred that the propylene homopolymer according tothis invention has no glass transition temperature below −30, preferablybelow −25° C., more preferably below −20° C.

On the other hand, in one preferred embodiment the propylene homopolymeraccording to this invention has a glass transition temperature in therange of −12 to 5° C., more preferably in the range of −10 to 4° C.

Further, the propylene homopolymer is preferably a crystalline. The term“crystalline” indicates that the propylene homopolymer has a rather highmelting temperature. Accordingly throughout the invention the propylenehomopolymer is regarded as crystalline unless otherwise indicated.Therefore the propylene homopolymer preferably has a melting temperaturemeasured by differential scanning calorimetry (DSC) of equal or morethan 160° C., i.e. of equal or more than 160 to 168° C., more preferablyof at least 161° C., i.e. in the range of 161 to 166° C.

Further it is preferred that the propylene homopolymer has acrystallization temperature measured by differential scanningcalorimetry (DSC) of equal or more than 114° C., more preferably in therange of 114 to 128° C., more preferably in the range of 118 to 126° C.

The propylene homopolymer is further featured by high stiffness.Accordingly the instant propylene homopolymer has a rather high tensilemodulus. Accordingly it is preferred that propylene homopolymer has atensile modulus measured at 23° C. according to ISO 527-1 (cross headspeed 1 mm/min) of at least 1,400 MPa, more preferably in the range of1,400 to 2,000 MPa, still more preferably in the range of 1,500 to 1,800MPa.

Preferably the propylene homopolymer according to this invention doesnot contain a 1,3,5 triazine derivatives of formula (I)

wherein

R′ and R″ are independently selected from the group, NHZ′, NZ′Z″, C1 toC10 alkyl, phenyl, and benzyl

Z′ and Z″ are independently selected from the group H, methyl, ethyl,n-propyl, iso-propyl, n-butyl, tert-butyl, and n-pentyl.

Preferably the propylene homopolymer according to this invention doesnot contain a hydrophobic aluminium silicate molecular sieve having anSi/Al molar ratio in the crystal lattice above 35, a pore diameter of atleast 5.5 A and a sorption capacity for water at 250° C. and 4.6 torr ofless than 10 wt.-%. Even more preferably the propylene homopolymeraccording to this invention does not contain a (hydrophobic) aluminiumsilicate.

Preferably the propylene homopolymer is obtained by polymerizingpropylene in the presence of a Ziegler-Natta catalyst as defined in moredetail below. Still more preferably the propylene homopolymer accordingto this invention is obtained by a process as defined in detail below byusing the Ziegler-Natta catalyst as defined herein.

The invention is also directed to an article comprising the propylenehomopolymer. Preferably the article comprises based on the total amountof the article at least 50 wt.-%, like 50 to 99.9 wt.-%, more preferablyat least 60 wt.-%, like 60 to 99 wt.-%, still more preferably 70 wt.-%,like 70 to 99.9 wt.-%, of the propylene homopolymer.

Preferably the article is an extruded article, like a film, or aninjection moulded article. In one embodiment the article can be also ablow moulded article, like an injection blow moulded article.

The propylene homopolymer according to this invention (as describedbelow) can comprises, more preferably can consist of, two fractions,namely a first propylene homopolymer fraction (H-PP1) and a secondpropylene homopolymer fraction (H-PP2). Preferably the weight ratiobetween the first propylene homopolymer fraction (H-PP1) and the secondpropylene homopolymer fraction (H-PP2) [(H-PP1):(H-PP2)] is 70:30 to40:60, more preferably 65:35 to 45:55.

The first propylene homopolymer fraction (H-PP1) and the secondpropylene homopolymer fraction (H-PP2) may differ in the melt flow rate.However it is preferred that the melt flow rate MFR₂ (230° C.) of thefirst propylene homopolymer fraction (H-PP1) and of the second propylenehomopolymer fraction (H-PP2) are nearby identical, i.e. differ not morethan 15% as calculated from the lower of the two values, preferablydiffer not more than 10%, like differ not more than 7%.

The propylene homopolymer as defined in the instant invention maycontain up to 5.0 wt.-% additives (except the triazine derivatives asmentioned above), like antioxidants, slip agents and antiblockingagents. Preferably the additive content is below 3.0 wt.-%, like below1.0 wt.-%.

In case the propylene homopolymer comprises a α-nucleating agent, it ispreferred that it is free of β-nucleating agents. The α-nucleating agentis preferably selected from the group consisting of

-   (i) salts of monocarboxylic acids and polycarboxylic acids, e.g.    sodium benzoate or aluminum tert-butylbenzoate, and-   (ii) dibenzylidenesorbitol (e.g. 1,3:2,4 dibenzylidenesorbitol) and    C₁-C₈-alkyl-substituted dibenzylidenesorbitol derivatives, such as    methyldibenzylidenesorbitol, ethyldibenzylidenesorbitol or    dimethyldibenzylidenesorbitol (e.g. 1,3:2,4 di(methylbenzylidene)    sorbitol), or substituted nonitol-derivatives, such as    1,2,3,-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)methylene]-nonitol,    and-   (iii) salts of diesters of phosphoric acid, e.g. sodium    2,2′-methylenebis(4, 6,-di-tert-butylphenyl) phosphate or    aluminium-hydroxy-bis[2,2′-methylene-bis(4,6-di-t-butylphenyl)phosphate],    and-   (iv) vinylcycloalkane polymer and vinylalkane polymer (as discussed    in more detail below), and-   (v) mixtures thereof.

Such additives are generally commercially available and are described,for example, in “Plastic Additives Handbook”, pages 871 to 873, 5thedition, 2001 of Hans Zweifel.

Preferably the propylene homopolymer contains up to 3 wt.-% of theα-nucleating agent. In a preferred embodiment, the propylene homopolymercontains not more than 2000 ppm, more preferably of 5 to 1500 ppm, morepreferably of 50 to 1000 ppm of a α-nucleating agent, in particularselected from the group consisting of dibenzylidenesorbitol (e.g.1,3:2,4 dibenzylidene sorbitol), dibenzylidenesorbitol derivative,preferably dimethyldibenzylidenesorbitol (e.g. 1,3:2,4di(methylbenzylidene) sorbitol), or substituted nonitol-derivatives,such as1,2,3,-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)methylene]-nonitol,sodium 2,2′-methylenebis(4, 6,-di-tert-butylphenyl) phosphate,vinylcycloalkane polymer, vinylalkane polymer, and mixtures thereof

In the following the manufacture of the propylene homopolymer isdescribed in more detail.

The propylene homopolymer according to this invention is preferablyproduced the presence of

-   (a) a Ziegler-Natta catalyst (ZN-C) comprising compounds (TC) of a    transition metal of Group 4 to 6 of IUPAC, a Group 2 metal    compound (MC) and an internal donor (ID), wherein said internal    donor (ID) is a non-phthalic compound, preferably is a non-phthalic    acid ester;-   (b) optionally a co-catalyst (Co), and-   (c) optionally an external donor (ED).

More preferably, the propylene homopolymer is produced in a sequentialpolymerization process comprising at least two reactors (R1) and (R2),in the first reactor (R1) the first propylene homopolymer fraction(H-PP1) is produced and subsequently transferred into the second reactor(R2), in the second reactor (R2) the second propylene homopolymerfraction (H-PP2) is produced in the presence of the first propylenehomopolymer fraction (H-PP1).

The term “sequential polymerization system” indicates that the propylenehomopolymer is produced in at least two reactors connected in series.Accordingly the present polymerization system comprises at least a firstpolymerization reactor (R1) and a second polymerization reactor (R2),and optionally a third polymerization reactor (R3). The term“polymerization reactor” shall indicate that the main polymerizationtakes place. Thus in case the process consists of two polymerizationreactors, this definition does not exclude the option that the overallsystem comprises for instance a pre-polymerization step in apre-polymerization reactor. The term “consist of” is only a closingformulation in view of the main polymerization reactors.

Preferably at least one of the two polymerization reactors (R1) and (R2)is a gas phase reactor (GPR). Still more preferably the secondpolymerization reactor (R2) and the optional third polymerizationreactor (R3) are gas phase reactors (GPRs), i.e. a first gas phasereactor (GPR1) and a second gas phase reactor (GPR2). A gas phasereactor (GPR) according to this invention is preferably a fluidized bedreactor, a fast fluidized bed reactor or a settled bed reactor or anycombination thereof

Accordingly, the first polymerization reactor (R1) is preferably aslurry reactor (SR) and can be any continuous or simple stirred batchtank reactor or loop reactor operating in bulk or slurry. Bulk means apolymerization in a reaction medium that comprises of at least 60% (w/w)monomer. According to the present invention the slurry reactor (SR) ispreferably a (bulk) loop reactor (LR). Accordingly the averageconcentration of the first fraction (1^(st) F) of the propylenehomopolymer (i.e. the first propylene homopolymer fraction (H-PP1)), inthe polymer slurry within the loop reactor (LR) is typically from 15wt.-% to 55 wt.-%, based on the total weight of the polymer slurrywithin the loop reactor (LR). In one preferred embodiment of the presentinvention the average concentration of the first propylene homopolymerfraction (H-PP1) in the polymer slurry within the loop reactor (LR) isfrom 20 wt.-% to 55 wt.-% and more preferably from 25 wt.-% to 52 wt.-%,based on the total weight of the polymer slurry within the loop reactor(LR).

Preferably the propylene homopolymer of the first polymerization reactor(R1), i.e. the first propylene homopolymer fraction (H-PP1), morepreferably the polymer slurry of the loop reactor (LR) containing thefirst propylene homopolymer fraction (H-PP1), is directly fed into thesecond polymerization reactor (R2), i.e. into the (first) gas phasereactor (GPR1), without a flash step between the stages. This kind ofdirect feed is described in EP 887379 A, EP 887380 A, EP 887381 A and EP991684 A. By “direct feed” is meant a process wherein the content of thefirst polymerization reactor (R1), i.e. of the loop reactor (LR), thepolymer slurry comprising the the first propylene homopolymer fraction(H-PP1), is led directly to the next stage gas phase reactor.

Alternatively, the propylene homopolymer of the first polymerizationreactor (R1), i.e. the first propylene homopolymer fraction (H-PP1),more preferably polymer slurry of the loop reactor (LR) containing thefirst propylene homopolymer fraction (H-PP1), may be also directed intoa flash step or through a further concentration step before fed into thesecond polymerization reactor (R2), i.e. into the gas phase reactor(GPR). Accordingly, this “indirect feed” refers to a process wherein thecontent of the first polymerization reactor (R1), of the loop reactor(LR), i.e. the polymer slurry, is fed into the second polymerizationreactor (R2), into the (first) gas phase reactor (GPR1), via a reactionmedium separation unit and the reaction medium as a gas from theseparation unit.

More specifically, the second polymerization reactor (R2), and anysubsequent reactor, for instance the third polymerization reactor (R3),are preferably gas phase reactors (GPRs). Such gas phase reactors (GPR)can be any mechanically mixed or fluid bed reactors.

Preferably the gas phase reactors (GPRs) comprise a mechanicallyagitated fluid bed reactor with gas velocities of at least 0.2 m/sec.Thus it is appreciated that the gas phase reactor is a fluidized bedtype reactor preferably with a mechanical stirrer.

Thus in a preferred embodiment the first polymerization reactor (R1) isa slurry reactor (SR), like loop reactor (LR), whereas the secondpolymerization reactor (R2) and any optional subsequent reactor, likethe third polymerization reactor (R3), are gas phase reactors (GPRs).Accordingly for the instant process at least two, preferably twopolymerization reactors (R1) and (R2) or three polymerization reactors(R1), (R2) and (R3), namely a slurry reactor (SR), like loop reactor(LR) and a (first) gas phase reactor (GPR1) and optionally a second gasphase reactor (GPR2), connected in series are used. If needed prior tothe slurry reactor (SR) a pre-polymerization reactor is placed.

The Ziegler-Natta catalyst (ZN-C) is fed into the first polymerizationreactor (R1) and is transferred with the polymer (slurry) obtained inthe first polymerization reactor (R1) into the subsequent reactors. Ifthe process covers also a pre-polymerization step it is preferred thatall of the Ziegler-Natta catalyst (ZN-C) is fed in thepre-polymerization reactor. Subsequently the pre-polymerization productcontaining the Ziegler-Natta catalyst (ZN-C) is transferred into thefirst polymerization reactor (R1).

A preferred multistage process is a “loop-gas phase”-process, such asdeveloped by Borealis A/S, Denmark (known as BORSTAR® technology)described e.g. in patent literature, such as in EP 0 887 379, WO92/12182 WO 2004/000899, WO 2004/111095, WO 99/24478, WO 99/24479 or inWO 00/68315.

A further suitable slurry-gas phase process is the Spheripol® process ofBasell.

Especially good results are achieved in case the temperature in thereactors is carefully chosen.

Accordingly it is preferred that the operating temperature in the firstpolymerization reactor (R1) is in the range of 62 to 85° C., morepreferably in the range of 65 to 82° C., still more preferably in therange of 67 to 80° C.

Alternatively or additionally to the previous paragraph it is preferredthat the operating temperature in the second polymerization reactor (R2)and optional in the third reactor (R3) is in the range of 75 to 95° C.,more preferably in the range of 78 to 92° C.

Preferably the operating temperature in the second polymerizationreactor (R2) is equal or higher to the operating temperature in thefirst polymerization reactor (R1). Accordingly it is preferred that theoperating temperature

(a) in the first polymerization reactor (R1) is in the range of 62 to85° C., more preferably in the range of 65 to 85° C., still morepreferably in the range of 67 to 82° C., like 70 to 80° C.;

and

(b) in the second polymerization reactor (R2) is in the range of 75 to95° C., more preferably in the range of 78 to 92° C., still morepreferably in the range of 78 to 88° C., with the proviso that theoperating temperature in the in the second polymerization reactor (R2)is equal or higher to the operating temperature in the firstpolymerization reactor (R1).

Typically the pressure in the first polymerization reactor (R1),preferably in the loop reactor (LR), is in the range of from 20 to 80bar, preferably 30 to 70 bar, like 35 to 65 bar, whereas the pressure inthe second polymerization reactor (R2), i.e. in the (first) gas phasereactor (GPR1), and optionally in any subsequent reactor, like in thethird polymerization reactor (R3), e.g. in the second gas phase reactor(GPR2), is in the range of from 5 to 50 bar, preferably 15 to 40 bar.

Preferably hydrogen is added in each polymerization reactor in order tocontrol the molecular weight, i.e. the melt flow rate MFR₂.

Preferably the average residence time is rather long in thepolymerization reactors (R1) and (R2). In general, the average residencetime (τ) is defined as the ratio of the reaction volume (V_(R)) to thevolumetric outflow rate from the reactor (Q_(o)) (i.e. V_(R)/Q_(o)),i.e. τ=V_(R)/Q_(o) [tau=V_(R)/Q_(o)]. In case of a loop reactor thereaction volume (V_(R)) equals to the reactor volume.

Accordingly the average residence time (τ) in the first polymerizationreactor (R1) is preferably at least 15 min, more preferably in the rangeof 15 to 80 min, still more preferably in the range of 20 to 60 min,like in the range of 24 to 50 min, and/or the average residence time (τ)in the second polymerization reactor (R2) is preferably at least 70 min,more preferably in the range of 70 to 220 min, still more preferably inthe range of 80 to 210 min, yet more preferably in the range of 90 to200 min, like in the range of 90 to 190 min. Preferably the averageresidence time (τ) in the third polymerization reactor (R3)—ifpresent—is preferably at least 30 min, more preferably in the range of30 to 120 min, still more preferably in the range of 40 to 100 min, likein the range of 50 to 90 min

As mentioned above the instant process can comprises in addition to the(main) polymerization of the propylene homopolymer in the at least twopolymerization reactors (R1, R3 and optional R3) prior thereto apre-polymerization in a pre-polymerization reactor (PR) upstream to thefirst polymerization reactor (R1).

In the pre-polymerization reactor (PR) a polypropylene (Pre-PP) isproduced. The pre-polymerization is conducted in the presence of theZiegler-Natta catalyst (ZN-C). According to this embodiment theZiegler-Natta catalyst (ZN-C), the co-catalyst (Co), and the externaldonor (ED) are all introduced to the pre-polymerization step. However,this shall not exclude the option that at a later stage for instancefurther co-catalyst (Co) and/or external donor (ED) is added in thepolymerization process, for instance in the first reactor (R1). In oneembodiment the Ziegler-Natta catalyst (ZN-C), the co-catalyst (Co), andthe external donor (ED) are only added in the pre-polymerization reactor(PR), if a pre-polymerization is applied.

The pre-polymerization reaction is typically conducted at a temperatureof 0 to 60° C., preferably from 15 to 50° C., and more preferably from20 to 45° C.

The pressure in the pre-polymerization reactor is not critical but mustbe sufficiently high to maintain the reaction mixture in liquid phase.Thus, the pressure may be from 20 to 100 bar, for example 30 to 70 bar.

In a preferred embodiment, the pre-polymerization is conducted as bulkslurry polymerization in liquid propylene, i.e. the liquid phase mainlycomprises propylene, with optionally inert components dissolved therein.Furthermore, according to the present invention, an ethylene feed isemployed during pre-polymerization as mentioned above.

It is possible to add other components also to the pre-polymerizationstage. Thus, hydrogen may be added into the pre-polymerization stage tocontrol the molecular weight of the polypropylene (Pre-PP) as is knownin the art. Further, antistatic additive may be used to prevent theparticles from adhering to each other or to the walls of the reactor.

The precise control of the pre-polymerization conditions and reactionparameters is within the skill of the art.

Due to the above defined process conditions in the pre-polymerization,preferably a mixture (MI) of the Ziegler-Natta catalyst (ZN-C) and thepolypropylene (Pre-PP) produced in the pre-polymerization reactor (PR)is obtained. Preferably the Ziegler-Natta catalyst (ZN-C) is (finely)dispersed in the polypropylene (Pre-PP). In other words, theZiegler-Natta catalyst (ZN-C) particles introduced in thepre-polymerization reactor (PR) split into smaller fragments which areevenly distributed within the growing polypropylene (Pre-PP). The sizesof the introduced Ziegler-Natta catalyst (ZN-C) particles as well as ofthe obtained fragments are not of essential relevance for the instantinvention and within the skilled knowledge.

As mentioned above, if a pre-polymerization is used, subsequent to saidpre-polymerization, the mixture (MI) of the Ziegler-Natta catalyst(ZN-C) and the polypropylene (Pre-PP) produced in the pre-polymerizationreactor (PR) is transferred to the first reactor (R1). Typically thetotal amount of the polypropylene (Pre-PP) in the final propylenecopolymer (R-PP) is rather low and typically not more than 5.0 wt.-%,more preferably not more than 4.0 wt.-%, still more preferably in therange of 0.5 to 4.0 wt.-%, like in the range 1.0 of to 3.0 wt.-%.

In case that pre-polymerization is not used propylene and the otheringredients such as the Ziegler-Natta catalyst (ZN-C) are directlyintroduced into the first polymerization reactor (R1).

Accordingly the process according the instant invention comprises thefollowing steps under the conditions set out above

(a) in the first polymerization reactor (R1), i.e. in a loop reactor(LR), propylene is polymerized obtaining a first propylene homopolymerfraction (H-PP1) of the propylene homopolymer (H-PP),

(b) transferring said first propylene homopolymer fraction (H-PP1) to asecond polymerization reactor (R2),

(c) in the second polymerization reactor (R2) propylene is polymerizedin the presence of the first propylene homopolymer fraction (H-PP1)obtaining a second propylene homopolymer fraction (H-PP2) of thepropylene homopolymer, said first propylene homopolymer fraction (H-PP1)and said second propylene homopolymer fraction (H-PP2) form thepropylene homopolymer.

A pre-polymerization as described above can be accomplished prior tostep (a).

The Ziegler-Natta Catalyst (ZN-C), the External Donor (ED) and theCo-Catalyst (Co)

As pointed out above in the specific process for the preparation of thepropylene copolymer (R-PP) as defined above a Ziegler-Natta catalyst(ZN-C) must be used. Accordingly the Ziegler-Natta catalyst (ZN-C) willbe now described in more detail.

The catalyst used in the present invention is a solid Ziegler-Nattacatalyst (ZN-C), which comprises compounds (TC) of a transition metal ofGroup 4 to 6 of IUPAC, like titanium, a Group 2 metal compound (MC),like a magnesium, and an internal donor (ID) being a non-phthaliccompound, preferably a non-phthalic acid ester, still more preferablybeing a diester of non-phthalic dicarboxylic acids as described in moredetail below. Thus, the catalyst is fully free of undesired phthaliccompounds. Further, the solid catalyst is free of any external supportmaterial, like silica or MgCl₂, but the catalyst is self-supported.

The Ziegler-Natta catalyst (ZN-C) can be further defined by the way asobtained. Accordingly the Ziegler-Natta catalyst (ZN-C) is preferablyobtained by a process comprising the steps of

-   a)    -   a₁) providing a solution of at least a Group 2 metal alkoxy        compound (Ax) being the reaction product of a Group 2 metal        compound (MC) and an alcohol (A) comprising in addition to the        hydroxyl moiety at least one ether moiety optionally in an        organic liquid reaction medium;    -   or    -   a₂) a solution of at least a Group 2 metal alkoxy compound (Ax′)        being the reaction product of a Group 2 metal compound (MC) and        an alcohol mixture of the alcohol (A) and a monohydric        alcohol (B) of formula ROH, optionally in an organic liquid        reaction medium;    -   or    -   a₃) providing a solution of a mixture of the Group 2 alkoxy        compound (Ax) and a Group 2 metal alkoxy compound (Bx) being the        reaction product of a Group 2 metal compound (MC) and the        monohydric alcohol (B), optionally in an organic liquid reaction        medium; and-   b) adding said solution from step a) to at least one compound (TC)    of a transition metal of Group 4 to 6 and-   c) obtaining the solid catalyst component particles,

and adding a non-phthalic internal electron donor (ID) at any step priorto step c).

The internal donor (ID) or precursor thereof is added preferably to thesolution of step a).

According to the procedure above the Ziegler-Natta catalyst (ZN-C) canbe obtained via precipitation method or via emulsion (liquid/liquidtwo-phase system)—solidification method depending on the physicalconditions, especially temperature used in steps b) and c).

In both methods (precipitation or emulsion-solidification) the catalystchemistry is the same.

In precipitation method combination of the solution of step a) with atleast one transition metal compound (TC) in step b) is carried out andthe whole reaction mixture is kept at least at 50° C., more preferablyin the temperature range of 55 to 110° C., more preferably in the rangeof 70 to 100° C., to secure full precipitation of the catalyst componentin form of a solid particles (step c).

In emulsion-solidification method in step b) the solution of step a) istypically added to the at least one transition metal compound (TC) at alower temperature, such as from −10 to below 50° C., preferably from −5to 30° C. During agitation of the emulsion the temperature is typicallykept at −10 to below 40° C., preferably from −5 to 30° C. Droplets ofthe dispersed phase of the emulsion form the active catalystcomposition. Solidification (step c) of the droplets is suitably carriedout by heating the emulsion to a temperature of 70 to 150° C.,preferably to 80 to 110° C.

The catalyst prepared by emulsion-solidification method is preferablyused in the present invention.

In a preferred embodiment in step a) the solution of a₂) or a₃) areused, i.e. a solution of (Ax′) or a solution of a mixture of (Ax) and(Bx).

Preferably the Group 2 metal (MC) is magnesium.

The magnesium alkoxy compounds (Ax), (Ax′) and (Bx) can be prepared insitu in the first step of the catalyst preparation process, step a), byreacting the magnesium compound with the alcohol(s) as described above,or said magnesium alkoxy compounds can be separately prepared magnesiumalkoxy compounds or they can be even commercially available as readymagnesium alkoxy compounds and used as such in the catalyst preparationprocess of the invention.

Illustrative examples of alcohols (A) are monoethers of dihydricalcohols (glycol monoethers). Preferred alcohols (A) are C₂ to C₄ glycolmonoethers, wherein the ether moieties comprise from 2 to 18 carbonatoms, preferably from 4 to 12 carbon atoms. Preferred examples are2-(2-ethylhexyloxy)ethanol, 2-butyloxy ethanol, 2-hexyloxy ethanol and1,3-propylene-glycol-monobutyl ether, 3-butoxy-2-propanol, with2-(2-ethylhexyloxy)ethanol and 1,3-propylene-glycol-monobutyl ether,3-butoxy-2-propanol being particularly preferred.

Illustrative monohydric alcohols (B) are of formula ROH, with R beingstraight-chain or branched C₆-C₁₀ alkyl residue. The most preferredmonohydric alcohol is 2-ethyl-1-hexanol or octanol.

Preferably a mixture of Mg alkoxy compounds (Ax) and (Bx) or mixture ofalcohols (A) and (B), respectively, are used and employed in a moleratio of Bx:Ax or B:A from 8:1 to 2:1, more preferably 5:1 to 3:1.

Magnesium alkoxy compound may be a reaction product of alcohol(s), asdefined above, and a magnesium compound selected from dialkylmagnesiums, alkyl magnesium alkoxides, magnesium dialkoxides, alkoxymagnesium halides and alkyl magnesium halides. Alkyl groups can be asimilar or different C₁-C₂₀ alkyl, preferably C₂-C₁₀ alkyl. Typicalalkyl-alkoxy magnesium compounds, when used, are ethyl magnesiumbutoxide, butyl magnesium pentoxide, octyl magnesium butoxide and octylmagnesium octoxide. Preferably the dialkyl magnesiums are used. Mostpreferred dialkyl magnesiums are butyl octyl magnesium or butyl ethylmagnesium.

It is also possible that magnesium compound can react in addition to thealcohol (A) and alcohol (B) also with a polyhydric alcohol (C) offormula R″ (OH)_(m) to obtain said magnesium alkoxide compounds.Preferred polyhydric alcohols, if used, are alcohols, wherein R″ is astraight-chain, cyclic or branched C₂ to C₁₀ hydrocarbon residue, and mis an integer of 2 to 6.

The magnesium alkoxy compounds of step a) are thus selected from thegroup consisting of magnesium dialkoxides, diaryloxy magnesiums,alkyloxy magnesium halides, aryloxy magnesium halides, alkyl magnesiumalkoxides, aryl magnesium alkoxides and alkyl magnesium aryloxides. Inaddition a mixture of magnesium dihalide and a magnesium dialkoxide canbe used.

The solvents to be employed for the preparation of the present catalystmay be selected among aromatic and aliphatic straight chain, branchedand cyclic hydrocarbons with 5 to 20 carbon atoms, more preferably 5 to12 carbon atoms, or mixtures thereof. Suitable solvents include benzene,toluene, cumene, xylol, pentane, hexane, heptane, octane and nonane.Hexanes and pentanes are particular preferred.

Mg compound is typically provided as a 10 to 50 wt-% solution in asolvent as indicated above. Typical commercially available Mg compound,especially dialkyl magnesium solutions are 20-40 wt-% solutions intoluene or heptanes.

The reaction for the preparation of the magnesium alkoxy compound may becarried out at a temperature of 40° to 70° C. Most suitable temperatureis selected depending on the Mg compound and alcohol(s) used.

The transition metal compound of Group 4 to 6 is preferably a titaniumcomound, most preferably a titanium halide, like TiCl₄.

The internal donor (ID) used in the preparation of the catalyst used inthe present invention is preferably selected from (di)esters ofnon-phthalic carboxylic (di)acids, 1,3-diethers, derivatives andmixtures thereof. Especially preferred donors are diesters ofmono-unsaturated dicarboxylic acids, in particular esters belonging to agroup comprising malonates, maleates, succinates, citraconates,glutarates, cyclohexene-1,2-dicarboxylates and benzoates, and anyderivatives and/or mixtures thereof. Preferred examples are e.g.substituted maleates and citraconates, most preferably citraconates.

In emulsion method, the two phase liquid-liquid system may be formed bysimple stirring and optionally adding (further) solvent(s) andadditives, such as the turbulence minimizing agent (TMA) and/or theemulsifying agents and/or emulsion stabilizers, like surfactants, whichare used in a manner known in the art for facilitating the formation ofand/or stabilize the emulsion. Preferably, surfactants are acrylic ormethacrylic polymers. Particular preferred are unbranched C₁₂ to C₂₀(meth)acrylates such as poly(hexadecyl)-methacrylate andpoly(octadecyl)-methacrylate and mixtures thereof. Turbulence minimizingagent (TMA), if used, is preferably selected from α-olefin polymers ofα-olefin monomers with 6 to 20 carbon atoms, like polyoctene,polynonene, polydecene, polyundecene or polydodecene or mixturesthereof. Most preferable it is polydecene.

The solid particulate product obtained by precipitation oremulsion-solidification method may be washed at least once, preferablyat least twice, most preferably at least three times with a aromaticand/or aliphatic hydrocarbons, preferably with toluene, heptane orpentane. The catalyst can further be dried, as by evaporation orflushing with nitrogen, or it can be slurried to an oily liquid withoutany drying step.

The finally obtained Ziegler-Natta catalyst is desirably in the form ofparticles having generally an average particle size range of 5 to 200μm, preferably 10 to 100. Particles are compact with low porosity andhave surface area below 20 g/m², more preferably below 10 g/m².Typically the amount of Ti is 1 to 6 wt-%, Mg 10 to 20 wt-% and donor 10to 40 wt-% of the catalyst composition.

Detailed description of preparation of catalysts is disclosed in WO2012/007430, EP2610271, EP 261027 and EP2610272 which are incorporatedhere by reference.

The Ziegler-Natta catalyst (ZN-C) is preferably used in association withan alkyl aluminum cocatalyst and optionally external donors.

As further component in the instant polymerization process an externaldonor (ED) is preferably present. Suitable external donors (ED) includecertain silanes, ethers, esters, amines, ketones, heterocyclic compoundsand blends of these. It is especially preferred to use a silane. It ismost preferred to use silanes of the general formulaR^(a) _(p)R^(b) _(q)Si(OR^(c))_((4-p-q))

wherein R^(a), R^(b) and R^(c) denote a hydrocarbon radical, inparticular an alkyl or cycloalkyl group, and wherein p and q are numbersranging from 0 to 3 with their sum p+q being equal to or less than 3.R^(a), R^(b) and R^(c) can be chosen independently from one another andcan be the same or different. Specific examples of such silanes are(tert-butyl)₂Si(OCH₃)₂, (cyclohexyl)(methyl)Si(OCH₃)²,(phenyl)₂Si(OCH₃)₂ and (cyclopentyl)₂Si(OCH₃)₂, or of general formulaSi(OCH₂CH₃)₃(NR³R⁴)

wherein R³ and R⁴ can be the same or different a represent a hydrocarbongroup having 1 to 12 carbon atoms.

R³ and R⁴ are independently selected from the group consisting of linearaliphatic hydrocarbon group having 1 to 12 carbon atoms, branchedaliphatic hydrocarbon group having 1 to 12 carbon atoms and cyclicaliphatic hydrocarbon group having 1 to 12 carbon atoms. It is inparticular preferred that R³ and R⁴ are independently selected from thegroup consisting of methyl, ethyl, n-propyl, n-butyl, octyl, decanyl,iso-propyl, iso-butyl, iso-pentyl, tert.-butyl, tert.-amyl, neopentyl,cyclopentyl, cyclohexyl, methylcyclopentyl and cycloheptyl.

More preferably both R¹ and R² are the same, yet more preferably both R³and R⁴ are an ethyl group.

Especially preferred external donors (ED) are the pentyl dimethoxysilane donor (D-donor) or the cyclohexylmethyl dimethoxy silane donor(C-Donor), the latter especially preferred.

In addition to the Ziegler-Natta catalyst (ZN-C) and the optionalexternal donor (ED) a co-catalyst can be used. The co-catalyst ispreferably a compound of group 13 of the periodic table (IUPAC), e.g.organo aluminum, such as an aluminum compound, like aluminum alkyl,aluminum halide or aluminum alkyl halide compound. Accordingly in onespecific embodiment the co-catalyst (Co) is a trialkylaluminium, liketriethylaluminium (TEAL), dialkyl aluminium chloride or alkyl aluminiumdichloride or mixtures thereof. In one specific embodiment theco-catalyst (Co) is triethylaluminium (TEAL).

Advantageously, the triethyl aluminium (TEAL) has a hydride content,expressed as AlH₃, of less than 1.0 wt % with respect to the triethylaluminium (TEAL). More preferably, the hydride content is less than 0.5wt %, and most preferably the hydride content is less than 0.1 wt %.

Preferably the ratio between the co-catalyst (Co) and the external donor(ED) [Co/ED] and/or the ratio between the co-catalyst (Co) and thetransition metal (TM) [Co/TM] should be carefully chosen.

Accordingly

(a) the mol-ratio of co-catalyst (Co) to external donor (ED) [Co/ED]must be in the range of 5 to 45, preferably is in the range of 5 to 35,more preferably is in the range of 5 to 25; and optionally

(b) the mol-ratio of co-catalyst (Co) to titanium compound (TC) [Co/TC]must be in the range of above 80 to 500, preferably is in the range of100 to 350, still more preferably is in the range of 120 to 300.

In the following the present invention is further illustrated by meansof examples.

EXAMPLES A. Measuring Methods

The following definitions of terms and determination methods apply forthe above general description of the invention including the claims aswell as to the below examples unless otherwise defined.

Quantification of Microstructure by NMR Spectroscopy

Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used toquantify the isotacticity and regio-regularity of the propylenehomopolymers.

Quantitative ¹³C {¹H} NMR spectra were recorded in the solution-stateusing a Bruker Advance III 400 NMR spectrometer operating at 400.15 and100.62 MHz for ¹H and ¹³C respectively. All spectra were recorded usinga ¹³C optimised 10 mm extended temperature probehead at 125° C. usingnitrogen gas for all pneumatics.

For propylene homopolymers approximately 200 mg of material wasdissolved in 1,2-tetrachloroethane-d₂ (TCE-d₂). To ensure a homogenoussolution, after initial sample preparation in a heat block, the NMR tubewas further heated in a rotatary oven for at least 1 hour. Uponinsertion into the magnet the tube was spun at 10 Hz. This setup waschosen primarily for the high resolution needed for tacticitydistribution quantification (Busico, V., Cipullo, R., Prog. Polym. Sci.26 (2001) 443; Busico, V.; Cipullo, R., Monaco, G., Vacatello, M.,Segre, A. L., Macromolecules 30 (1997) 6251). Standard single-pulseexcitation was employed utilising the NOE and bi-level WALTZ16decoupling scheme (Zhou, Z., Kuemmerle, R., Qiu, X., Redwine, D., Cong,R., Taha, A., Baugh, D. Winniford, B., J. Mag. Reson. 187 (2007) 225;Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J.,Talarico, G., Macromol. Rapid Commun. 2007, 28, 11289). A total of 8192(8 k) transients were acquired per spectra.

Quantitative ¹³C {¹H} NMR spectra were processed, integrated andrelevant quantitative properties determined from the integrals usingproprietary computer programs.

For propylene homopolymers all chemical shifts are internally referencedto the methyl isotactic pentad (mmmm) at 21.85 ppm.

Characteristic signals corresponding to regio defects (Resconi, L.,Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253; Wang,W-J., Zhu, S., Macromolecules 33 (2000), 1157; Cheng, H. N.,Macromolecules 17 (1984), 1950) or comonomer were observed.

The tacticity distribution was quantified through integration of themethyl region between 23.6-19.7 ppm correcting for any sites not relatedto the stereo sequences of interest (Busico, V., Cipullo, R., Prog.Polym. Sci. 26 (2001) 443; Busico, V., Cipullo, R., Monaco, G.,Vacatello, M., Segre, A. L., Macromolecules 30 (1997) 6251).

Specifically the influence of regio-defects and comonomer on thequantification of the tacticity distribution was corrected for bysubtraction of representative regio-defect and comonomer integrals fromthe specific integral regions of the stereo sequences.

The isotacticity was determined at the pentad level and reported as thepercentage of isotactic pentad (mmmm) sequences with respect to allpentad sequences:[mmmm]%=100*(mmmm/sum of all pentads)

The presence of 2,1 erythro regio-defects was indicated by the presenceof the two methyl sites at 17.7 and 17.2 ppm and confirmed by othercharacteristic sites. Characteristic signals corresponding to othertypes of regio-defects were not observed (Resconi, L., Cavallo, L.,Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253).

The amount of 2,1 erythro regio-defects was quantified using the averageintegral of the two characteristic methyl sites at 17.7 and 17.2 ppm:P _(21e)=(I _(e6) +I _(e8))/2

The amount of 1,2 primary inserted propene was quantified based on themethyl region with correction undertaken for sites included in thisregion not related to primary insertion and for primary insertion sitesexcluded from this region:P ₁₂ =I _(CH3) +P _(12e)

The total amount of propene was quantified as the sum of primaryinserted propene and all other present regio-defects:P _(total) =P ₁₂ +P _(21e)

The mole percent of 2,1 erythro regio-defects was quantified withrespect to all propene:[21e]mol.-%=100*(P _(21e) /P _(total))

MFR₂ (230° C./2.16 kg) is measured according to ISO 1133 (230° C., 2.16kg load)

The Xylene Soluble Fraction at Room Temperature (XS, Wt.-%):

The amount of the polymer soluble in xylene is determined at 25° C.according to ISO 16152; first edition; 2005-07-01.

DSC Analysis, Melting Temperature (T_(m)) and Heat of Fusion (H_(f)),Crystallization Temperature (T_(c)) and Heat of Crystallization (H_(c)):

measured with a TA Instrument Q200 differential scanning calorimetry(DSC) on 5 to 7 mg samples. DSC is run according to ISO 11357/part3/method C2 in a heat/cool/heat cycle with a scan rate of 10° C./min inthe temperature range of −30 to +225° C. Crystallization temperature andheat of crystallization (H_(c)) are determined from the cooling step,while melting temperature and heat of fusion (H_(f)) are determined fromthe second heating step p.

The glass transition temperature Tg is determined by dynamic mechanicalanalysis according to ISO 6721-7. The measurements are done in torsionmode on compression moulded samples (40×10×1 mm³) between −100° C. and+150° C. with a heating rate of 2° C./min and a frequency of 1 Hz.

Charpy Impact Test:

The Charpy notched impact strength (NIS) was measured according to ISO179 1 eA at +23° C., using injection molded bar test specimens of80×10×4 mm³ prepared in accordance with ISO 294-1:1996

Tensile Test:

The tensile modulus was measured at 23° C. according to ISO 527-1 (crosshead speed 1 mm/min) using injection moulded specimens moulded at 180°C. or 200° C. according to ISO 527-2(1B), produced according to EN ISO1873-2 (dog 10 bone shape, 4 mm thickness).

Total Volatiles

VOC

VOC was determined according to VDA 278:2002 from pellets or plates of60×60×2 mm³ prepared by injection molding in accordance with ISO294-1:1996.

VOC according to VDA 278 is the sum of all high and medium volatilecompounds. It is calculated as toluene equivalent (TE). VOC according toVDA 278 represents all organic compounds in the boiling point andelution range of up to C₂₀ (n-eicosane).

FOG

FOG was determined according to VDA 278:2002 from pellets or plates of60×60×2 mm³ prepared by injection molding in accordance with ISO294-1:1996.

FOG according to VDA 278 is the sum of all organic compounds of lowvolatility, which have an elution time greater than or equal ton-hexadecane. FOG is calculated as hexadecane equivalent (HE). FOGaccording to VDA 278 represents organic compounds in the boiling pointrange of n-alkanes C16 to C32.

VDA standards are issued by “Verband der Automobilindustrie”. The VDAstandards used herein are available from “Dokumentation Kraftfahrwesen(DKF); Ulrichstrasse 14, D-74321 Bietigheim-Bissingen, Germany or can bedownloaded from their website (www.dkf-ev.de).

B. Examples

The catalyst used in the polymerization process for the propylenehomopolymers of the inventive examples (IE1 to IE3) was prepared asfollows:

Used Chemicals:

20% solution in toluene of butyl ethyl magnesium (Mg(Bu)(Et), BEM),provided by Chemtura

2-ethylhexanol, provided by Amphochem

3-Butoxy-2-propanol—(DOWANOL™ PnB), provided by Dow

bis(2-ethylhexyl)citraconate, provided by SynphaBase

TiCl₄, provided by Millenium Chemicals

Toluene, provided by Aspokem

Viscoplex® 1-254, provided by Evonik

Heptane, provided by Chevron

Preparation of a Mg Alkoxy Compound

Mg alkoxide solution was prepared by adding, with stirring (70 rpm),into 11 kg of a 20 wt-% solution in toluene of butyl ethyl magnesium(Mg(Bu)(Et)), a mixture of 4.7 kg of 2-ethylhexanol and 1.2 kg ofbutoxypropanol in a 20 l stainless steel reactor. During the additionthe reactor contents were maintained below 45° C. After addition wascompleted, mixing (70 rpm) of the reaction mixture was continued at 60°C. for 30 minutes. After cooling to room temperature 2.3 kg g of thedonor bis(2-ethylhexyl)citraconate was added to the Mg-alkoxide solutionkeeping temperature below 25° C. Mixing was continued for 15 minutesunder stirring (70 rpm).

Preparation of Solid Catalyst Component

20.3 kg of TiCl₄ and 1.1 kg of toluene were added into a 20 l stainlesssteel reactor. Under 350 rpm mixing and keeping the temperature at 0°C., 14.5 kg of the Mg alkoxy compound prepared in example 1 was addedduring 1.5 hours. 1.7 l of Viscoplex® 1-254 and 7.5 kg of heptane wereadded and after 1 hour mixing at 0° C. the temperature of the formedemulsion was raised to 90° C. within 1 hour. After 30 minutes mixing wasstopped catalyst droplets were solidified and the formed catalystparticles were allowed to settle. After settling (1 hour), thesupernatant liquid was siphoned away. Then the catalyst particles werewashed with 45 kg of toluene at 90° C. for 20 minutes followed by twoheptane washes (30 kg, 15 min) During the first heptane wash thetemperature was decreased to 50° C. and during the second wash to roomtemperature.

The thus obtained catalyst was used along with triethyl-aluminium (TEAL)as co-catalyst and dicyclo pentyl dimethoxy silane (D-donor) orcyclohexylmethyl dimethoxy silane (C-Donor) as donor.

The catalyst used in the polymerization processes of the comparativeexamples (CE1 and CE2) was the catalyst Avant ZN M1 along withtriethyl-aluminium (TEAL) as co-catalyst and cyclohexylmethyl dimethoxysilane (C-donor) as donor.

The aluminium to donor ratio, the aluminium to titanium ratio and thepolymerization conditions are indicated in table 1.

TABLE 1 Preparation of the Examples CE1 CE2 IE1 IE2 IE3 Donor type C C CD C TEAL/Ti [mol/mol] 170 150 262 150 TEAL/Donor [mol/mol] 8.5 18.8 9.418.8 Loop (H-PP1) Time [h] 0.5 0.66 0.52 0.66 Temperature [° C.] 70 7575 75 MFR₂ [g/10 min] 80 77.0 81.0 198 XCS [wt.-%] 2.9 4.9 2.7 4.5 H₂/C3ratio [mol/kmol] 7.7 7.2 7.6 9.1 Amount [wt.-%] 50 100 50 100 1 GPR(H-PP2) Time [h] 0.5 — 1.97 — Temperature [° C.] 70 — 80 — H₂/C3 ratio[mol/kmol] 7.7 — 93.8 — Amount [wt.-%] 50 — 50 — Final MFR₂ [g/10 min]80 125 79 81 198 XCS [wt.-%] 2.9 2.8 4.9 2.8 4.5 Tm [° C.] 160 165 162.6165.0 162 Tc [° C.] 114 105 122.4 120.5 122 2, 1 [—] n.d n.d. n.d. n.dn.d. Mmmm [%] 93.3 93.3 93.5 96.5 93.4

CE2 is the commercial polypropylene homopolymer HK060AE available fromBorealis AG.

TABLE 2 Properties of the Examples Example CE1 CE2 IE1 IE2 IE3 MFR [g/10min] 80 125 79 81 198 Tm [° C.] 160 165 162.6 165.0 162 Tc [° C.] 114105 122.4 120.5 122 Tg [° C.] 2.0 2.5 2.0 2.0 2.5 XCS [wt.-%] 2.9 2.84.9 2.8 4.5 Tensile Modulus [MPa] 1441 1596 1701 1687 1569 Charpy NIS +23° C. [kJ/m²] 1.1 1.6 1.7 1.6 1.3 VOC (pellets) [ppm] 216 299 135 206144 FOG (pellets) [ppm] 455 607 418 483 568 VOC (plaques) [ppm] 281 —112 150 — FOG (plaques) [ppm] 594 — 410 413 —

The invention claimed is:
 1. A propylene homopolymer having (a) a meltflow rate MFR₂ (230° C./2.16 kg) measured according to ISO 1133 in therange of 75.0 to 500 g/10 min; and (b) a pentad isotacticity (mmmm) ofmore than 90.0% determined by ¹³C-NMR spectroscopy wherein further (c)the propylene homopolymer fulfills inequation (I)VOC≦(MFR×0.08)+201.0 wherein VOC is the amount of volatile organiccompounds (VOC) [in ppm] measured according to VDA 278:2002 of thepropylene homopolymer; MFR is the melt flow rate MFR₂ (230° C./2.16 kg)measured according to ISO 1133 of the propylene homopolymer, and (d) thepropylene homopolymer has a melting temperature Tm of equal to or morethan 160° C.
 2. The propylene homopolymer according to claim 1 having anamount of volatile organic compounds (VOC) measured according to VDA278:2002 of equal or below 210 ppm.
 3. The propylene homopolymeraccording to claim 1 having a crystallization temperature of equal to ormore than 114° C.
 4. The propylene homopolymer according to claim 1,having a xylene cold soluble content (XCS) determined according ISO16152 (25° C.) of at least 1.8 wt.-%.
 5. The propylene homopolymeraccording to claim 1, having 2,1 erythro regio-defects of equal to orbelow 0.4 mol.-% determined by ¹³C-NMR spectroscopy.
 6. The propylenehomopolymer according to claim 1, having a pentad isotacticity (mmmm) ofmore than 93.0%.
 7. The propylene homopolymer according to claim 1,fulfilling inequation (II)FOG≦(MFR×1.26)+350.0 wherein FOG is the amount of fogging compounds(FOG) [in ppm] measured according to VDA 278:2002 of the propylenehomopolymer; and MFR is the melt flow rate MFR₂ (230° C./2.16 kg)measured according to ISO 1133 of the propylene homopolymer.
 8. Thepropylene homopolymer according to claim 1, having an amount of foggingcompounds (FOG) measured according to VDA 278:2002 of not more than 580ppm.
 9. The propylene homopolymer according to claim 1, having a tensilemodulus measured at 23° C. according to ISO 527-1 (cross head speed 1mm/min) of at least 1,500 MPa.
 10. An article comprising the propylenehomopolymer according claim
 1. 11. A process for producing a propylenehomopolymer according to claim 1, wherein propylene has been polymerizedin the presence of (a) a Ziegler-Natta catalyst (ZN-C) comprisingcompounds (TC) of a transition metal of Group 4 to 6 of IUPAC, a Group 2metal compound (MC) and an internal donor (ID), wherein said internaldonor (ID) is a non-phthalic compound selected from optionallysubstituted glutarates and citraconate; (b) optionally a co-catalyst(Co), (c) optionally an external donor (ED), and (d) the molar-ratio ofco-catalyst (Co) to external donor (ED) [Co/ED] is 5 to
 45. 12. Theprocess according to claim 11, wherein the propylene homopolymer isproduced in a sequential polymerization process comprising at least tworeactors (R1) and (R2), in the first reactor (R1) a first propylenehomopolymer fraction (H-PP1) is produced and subsequently transferredinto the second reactor (R2), in the second reactor (R2) a secondpropylene homopolymer fraction (H-PP2) is produced in the presence ofthe first propylene homopolymer fraction (H-PP1).
 13. The propylenehomopolymer according to claim 2, having a crystallization temperatureof equal to or more than 114° C.
 14. The propylene homopolymer accordingto claim 2, having a xylene cold soluble content (XCS) determinedaccording ISO 16152 (25° C.) of at least 1.8 wt.-%.
 15. The propylenehomopolymer according to claim 2, having 2,1 erythro regio-defects ofequal to or below 0.4 mol.-% determined by ¹³C-NMR spectroscopy.
 16. Thepropylene homopolymer according to claim 2, having a pentad isotacticity(mmmm) of more than 93.0%.
 17. The propylene homopolymer according toclaim 2, fulfilling inequation (II)FOG≦(MFR×1.26)+350.0 wherein FOG is the amount of fogging compounds(FOG) [in ppm] measured according to VDA 278:2002 of the propylenehomopolymer; and MFR is the melt flow rate MFR₂ (230° C./2.16 kg)measured according to ISO 1133 of the propylene homopolymer.